<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        body {
            background-color: #bbb;
        }

        #canvas {
            background-color: #fff;
        }
    </style>
</head>

<body>
    <canvas id="canvas" width="400" height="400"></canvas>
    <textarea id="log"></textarea>
</body>
<script src="./utils.js"></script>
<script>
    window.onload = () => {
        var canvas = document.getElementById("canvas");
        var context = canvas.getContext("2d");
        var log = document.getElementById("log");

        var rect1 = {
            x: Math.random() * canvas.width,
            y: Math.random() * canvas.height,
        };
        context.fillStyle = "#000000";
        context.fillRect(rect1.x - 2, rect1.y - 2, 4, 4);

        var rect2 = {
            x: Math.random() * canvas.width,
            y: Math.random() * canvas.height,
        };
        context.fillStyle = "#ff0000";
        context.fillRect(rect2.x - 2, rect2.y - 2, 4, 4);

        var dx = rect1.x - rect2.x,
            dy = rect1.y - rect2.y,
            dist = Math.sqrt(dx * dx + dy * dy);

        log.value = "distance：" + dist;
    };
</script>

</html>